This invention relates to a motor vehicle having an anti-theft arrangement which blocks the starting of the engine. In motor vehicles of this type, the theft protection consists of the fact that the engine can be started only if an access-authorizing code signal is entered by the user, which causes the generation of a start release signal. A control unit permits the operation of the engine only when the start release signal is present, so that the vehicle can not be started without the possession of the valid access code.
An anti-theft measure of this type is described, for example, in the firm brochure "Diebstahlschutz fur das Auto" ("Theft Protection for the Automobile") of the firm TEMIC TELEFUNKEN microelectronic GmbH, printing date: August 1993. In that case, a transponder which is integrated into the car key transmits in a contactless manner specific data to an electronic analysis system whose receiver coil is integrated in the ignition lock.
German Patent Document DE-OS 23 58 211, discloses a protection circuit for ignition systems, in which unauthorized starting of the vehicle is prevented by interruption or disturbance of the ignition process, (particularly by the interruption of the ignition coil circuit), which interruption can be overridden by an electronic circuit situated partially in the ignition key and partially in the vehicle proper. Insertion of the ignition key into the ignition lock operates to override the previous disturbance of the ignition process.
U.S. Pat. No. 4,209,709 also discloses an anti-theft arrangement which operates by blocking the start of the engine. An anti-theft circuit has an input connected to the starting line originating from an ignition starting switch, and activates an engine start when it receives a start request signal generated by the closing of an ignition starting switch while it is in an engine-start releasing condition. The anti-theft circuit can be switched between the engine-start-releasing condition and an engine-start-blocking condition by means of an input code signal entered through the ignition starting switch itself as a defined sequence of switch-on and switch-off conditions, with predetermined time intervals required between successive switch conditions. The anti-theft circuit is adapted specifically to this code input implemented by way of the switch disposed in front of it. Logic elements, buffering trigger elements and time delay devices are utilized to pass a start request signal only if the predetermined switch condition sequence was recognized beforehand.
For anti-theft systems in motor vehicles, it is also known to use a central electronic control system of the motor vehicle, which also performs engine control functions. The control is inactive in an inoperative position, and can be switched-over to an active operating condition only by the entry of a predetermined user code by way of a user-side electronic key. See, for example, German Patent DE-OS 36 13 605 A1.
An object of the present invention is to provide a motor vehicle with a functionally reliable and secure protection against unauthorized starting of a vehicle engine, which is as protected from tampering or manipulation to the greatest extent possible, and can be implemented with low circuit-technological expenditures.
This object is achieved according to the invention by a motor vehicle anti-theft device in which the unit that generates the activating signal for the starter is used as the engine-start-blocking and releasing control unit, and the starting line (that is, the existing starting current path) is used to transmit the start release signal, so that no additional line is required. Such dual utilization of the starting line is possible because it otherwise carries current only during starter operation. Thus, at other times, (particularly before the operating of the ignition starting switch), it can be used to transmit other information. Another advantage of this arrangement is that the start release signal is transmitted by means of a connection which is necessary for starting the engine, so that if the connection fails the vehicle cannot be started. Thus, a separate failure of the anti-theft system (that is, failure to block an engine start) cannot occur.
In a further embodiment of the invention, a start release unit, which recognizes the start release signal, and a control unit, which activates the starter, are components of an electronic engine control system. This type of an anti-theft arrangement can thus be implemented by a small number of additional hardware and/or software measures on a conventional electronic engine control system.
For vehicles which already have an anti-theft system that recognizes the access authorization, a further embodiment of the invention is particularly advantageous in that the anti-theft system provides the start release system and feeds it to the starting line where it can be taken off by the control unit. Additional modules for providing the start release signal are therefore not required.